CLASSIFICATION OF THE YERTEBRATA. 39 



damp places ; which are destitute of plates or scales (in ex- 

 isting species ) ; which have three cavities in the heart ; nu- 

 cleated blood-corpuscles; and the skull with two occipital 

 condyles ; as Frogs and Toads, Salamandars, etc. 

 V. PISCES, or Fishes, or gill-breathing, cool-blooded animals, 

 which live in the water, and which in general lay eggs from 

 which their young are hatched ; and which have only two 

 cavities in the heart. 



These classes stand in the order of their rank, the first 

 named being the highest, and the last named the lowest. 



Many writers regard Reptiles and Batrachians as one 

 class, and call them all Eeptiles, thus making only four 

 classes of the Vertebrates.* They then subdivide this 

 class into Eeptiles proper and Amphibians. 



In all these classes the fundamental idea of the Verte- 

 brates is more or less plainly manifested, and the principal 

 parts of the skeleton in the different classes correspond to 

 one another, part to part, spinal column to spinal column, 

 and locomotive members to locomotive members; the 



Dr. Theodore Gill, in a recent paper (see American Jour, of Sci. and Art*, 

 3d Series, No. 36, Vol. VI.), recognizes eight classes in the Vertebrata. He 

 writes his classification thus : 

 Branch VERTEBRATA. 



A. Sub-branch CRANIOTA. 



Super-class MALLEIFERA. 



I. Class Mammalia. 

 Super-class QUADRATIFER^-. 



(Sauropsida.) 

 II. Class Aves. 



III. Class Reptilia. 



(Batrachopsida.) 



IV. Class Batrachia. 

 Super-class LYRIFERA. 



V. Class Pisces, 

 VI. Class Elasmobrnnchia. 

 Super-class MONORRHINA. 



VII. Class Marsipobranchia. 



B. Sub-branch A CRANIA. 



VIII. Class Leptocardii. 



